1. Field of the Invention
This invention relates to wireless wide area networks and, more particularly, to call admission control in such networks.
2. Discussion of Related Art
Subscribers are adopting wireless communications in increasingly large numbers. Wireless wide area networks service such calls via Mobile Switching Centers (MSC's), other switches, and other components.
To keep the MSCs and other switches from getting overloaded, the admission of new calls is controlled via a process known as “Call Admission Control.” In this fashion, some guarantee on call processing delay can be given to a very large percentage of the calls processed by the switch. For example, a quality of service (QoS) metric may be established (e.g., calls will suffer less than 200 ms of call setup latency), and through the control of new calls, the QoS metric can be guaranteed for call setups in progress. Call admission control involves reducing (or throttling) the call arrival. In short, with call admission control some calls are dropped before processing rather than potentially saturating the system by attempting to handle the call.
A conservative call admission control policy can prevent the switch from getting overloaded but at the expense of throughput. An aggressive call admission control policy can increase the throughput but may be unable to meet the QoS metric (as a consequence of not detecting congestion fast enough).
In a distributed system, throttling can be implemented in multiple ways based on the ability of the peer entity and the communication protocol among the entities. For example, the peer entity may be capable of receiving explicit feedback through the control/signaling protocol to reduce the call rate or the peer entity may have to implicitly infer from expired timers for calls that were not responded to by the switch. Some systems may effectively look at the most utilized component (i.e., the closest to being saturated) and throttle the calls accordingly.
To control call admissions, software logic is typically used to determine when the number of calls arriving into the switch or MSC is in danger of saturating the switch. The call admission control logic will “drop calls” to prevent such saturation. To date, many call admission control policies have been ad hoc. There is a need in the art for an improved method and system for controlling call admissions to the network.